import java.util.Scanner;

public class Sum {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int sum = 0;
        for (int i = 1; i <= n; i++) {
            int count = 1;
            for (int j = 1; j <= i; j++) {
                count = count*j;
            }
            sum += count;
        }
        System.out.println(sum);
    }
}
